Studies aimed at characterizing the discriminative stimulus properties of phencyclidine (PCP) will be continued in the rat and parallel studies will be initiated in the squirrel moneky. The hypothesis to be tested is that the components of action of PCP and related compounds that enable them to function as discriminative stimuli in animals are analogous to the components of action that engender subjective effects in man. Thus, drug discrimination paradigms could provide animal models for the preclinical identification and evaluation of the components of action of PCP and analogues that underlie their potential for abuse. Rats and squirrel monkeys will be trained to discriminate between saline and PCP in a two-choice discrete-trial avoidance paradigm. Stimulus generalization curves in both species will be determined for novel drugs including structural analogues of PCP, psychotomimetic opioid compounds, and representative compounds from other classes of psychoactive drugs. In addition, a variety of drugs will be tested for their ability to block the discriminative stimulus effects of PCP and compounds found to have PCP-like activity.